1. Field of the Invention
The present invention relates to a physical quality detecting device for detecting a physical quality supplied from the outside and to an imaging apparatus using a solid-state imaging device for detecting light incident from the outside as a physical quantity.
2. Description of the Related Art
A solid-state imaging device for detecting the intensity of light incident via a subject as a physical quantity or a fingerprint detecting device (capacitance detecting device) for detecting capacitance formed to correspond to a fingerprint between a detecting electrode and the surface of a finger has known a physical quantity detecting device for detecting a physical quantity supplied from the outside.
FIG. 1 is a diagram illustrating a pixel of a solid-state imaging device. As shown in FIG. 1, a pixel 100 includes a photodiode 101, serving as a photoelectric converter, and four transistors, that is, a transfer transistor 102, a reset transistor 103, an amplifying transistor 104, and a selecting transistor 105, which are connected to one vertical signal line 110. In this structure, N-channel MOS transistors are used as the four transistors 102 to 105.
The selecting transistor 105 is described below. The selecting transistor 105 serves as a switching element performing the selection/non-selection of the pixel 100. It is ideal that, when the selecting transistor 105 is turned on, resistance is zero regardless of a source-drain voltage, and when the selecting transistor 105 is turned off, the resistance has an infinite value regardless of the source-drain voltage.
However, actually, the source-drain voltage capable of turning on the selecting transistor 105 is limited, and the on-resistance is a finite value. In addition, since the selecting transistor 105 is connected in series to the amplifying transistor 104, the pixel 100 having the above-mentioned structure has the following two problems.
(1) Since a voltage drops due to a decrease in the threshold value of the selecting transistor 105, it is difficult to reduce a power supply voltage Vdd.
(2) Noise (for example, 1/f noise and burst noise) caused by the selecting transistor 105 occurs in the vertical signal line 110.
In particular, the 1/f noise and the burst noise cause a problem in a very small pixel. As shown in FIG. 2, the burst noise increases in a very small number of pixels among the pixels arranged in a line, or is randomly moved between a binary value and a ternary value in each pixel. The burst noise and the 1/f noise are more likely to result from the interaction between a channel and a gate oxide film of a transistor.
The 1/f noise is random noise occurring in a large number of pixels among all the pixels. The burst noise causes a very small number of pixels to appear to flicker. As described above, practically, the selecting transistor 105 is not an ideal switch, but has a finite on-resistance. Therefore, noise caused by the selecting transistor 105 as well as the noise of the amplifying transistor 104 occurs in the output.
In the related art, in order to solve the above-mentioned problem (1), the following structure has been proposed: a boosting circuit for raising the power supply voltage Vdd is provided in the same chip as that in which the pixels 100 are formed, and the voltage raised by the boosting circuit, that is, a voltage higher than the power supply voltage Vdd is applied to the selecting transistor 105 as agate voltage (for example, see Japanese Patent No. 3369911).